Cast wheel rim

ABSTRACT

A cast wheel rim ( 1 ) including a light-metal body ( 2 ) which at least partially encompasses at least one shaped part ( 8, 8′, 8″ ) forming a cast-in core and having a mean specific weight smaller than that of the light metal used for the casting, wherein the shaped part ( 8, 8′, 8″ ) is comprised of a pressed body made of a porous silicate material.

[0001] The invention relates to a cast wheel rim including a light-metalbody which at least partially encompasses at least one shaped partforming a cast-in core and having a mean specific weight smaller thanthat of the light metal used for the casting.

[0002] In order to reduce the dead weight of cast wheel rims, on the onehand, and to continue to safeguard a high strength of the wheel rim, onthe other hand, attempts have been made for quite some time to providein wheel rims hollow cores or lost cores having as low a specific deadweight as possible.

[0003] From DE 206 973 A, a wheel rim made of aluminum is known, inwhich various parts of the wheel are comprised of a hollow, resistantmetal such as, e.g., steel or the like, forming hollow cores and beingcast round by a light aluminum alloy.

[0004] It was likewise proposed (cf. e.g. DE 41 38 558 A) to producewheel rims with hollow spokes which are produced by the aid of sandcores in the mold tool, said sand cores being removed from the rim afterproduction.

[0005] Furthermore, a cast wheel rim is known from U.S. Pat. No. 3 253862 A, which is produced by casting aluminum around a lost corecomprised of metal wool.

[0006] WO 99/39923 A, moreover, describes a cast wheel rim in which acast-in core is provided to reduce the dead weight of the cast wheelrim, said core having a lower specific weight than the light metal usedfor the casting and to this end being, in particular, a core partcomprised of aluminum foam. The manufacture of such cast wheel rimsinvolves problems, because the core cannot be preheated to the castingtemperature and is heated as the light metal is being cast round, whichcauses gas present within said aluminum foam to expand, wherebystrength-reducing gas inclusions are likely to occur in the light-metalwheel rim body. Preheating of the core part to the temperature of theliquid light metal - as would be desirable in order to avoid theexpansion of enclosed air during the casting procedure - is not feasiblesince the aluminum-foam core part would loose its dimensional stability.

[0007] It is, therefore, the object of the invention to provide a castwheel rim having a low dead weight which does not entail saidmanufacturing engineering problems regarding the loss of dimensionalstability or the expanding gas of the shaped part, and to provide a castwheel rim that is easy to produce and offers a high strength.

[0008] The cast wheel rim of the initially defined kind is characterizedin that the shaped part is comprised of a pressed body made of a poroussilicate material.

[0009] By the aid of a shaped part made of a porous silicate material, acast-in core exhibiting a high temperature resistance is provided in thecast wheel rim, which can, thus, be preheated to at least substantiallythe casting temperature and will, therefore, remain dimensionally stableduring preheating; after preheating, no gas explosion will consequentlytake place as the light metal used for the casting is being cast round.Furthermore, no penetration of molten light metal into the openings ofthe porous material will occur on account of the structure of thesilicate material.

[0010] In order to be able to reliably ensure that the air enclosed inthe shaped part does not expand as the latter is being cast round, whichwould bring about strength-reducing gas inclusions in the light-metalbody and hence a high reject rate during manufacture, it is advantageousif the silicate material has a temperature resistance up to atemperature that is higher than the melting point of the light metalused for the casting. The shaped part can, thus, be readily preheated tothe temperature suitable for casting round, while retaining itsdimensional stability required for handling; yet, no further heating ofthe shaped part during casting and, of course, also no expansion of thegas enclosed in the porous shaped part during heating will occur.

[0011] Since, above all, aluminum is used in.the manufacture of castwheel rims, which is cast substantially at a temperature of 700° C., itis beneficial if the silicate material has a temperature resistance upto at least 1000° C. The shaped part, while maintaining its shaperequired for the manufacture of the cast wheel rim, can thus bepreheated to a temperature higher than the casting temperature of thelight metal. As a result, air enclosed in the porous silicate materialwill not expand further during casting and gas inclusions in thelight-metal body will not occur.

[0012] In order to provide a cost-effective shaped part that is easy toproduce in terms of manufacturing engineering and constitutes a cast-incore, it is advantageous if the silicate material is comprised of Al, Mgand/or Fe silicates. A material especially satisfying all requirementsas to temperature resistance, light-metal infiltration avoidance andcost efficiency is used for the shaped part if the silicate material iscomprised of silicate-bonded aluminum-iron-magnesium silicate. In orderto attain a wheel rim dead weight reduced in view of cast wheel rimshaving cast-in metal foam cores, it is advantageous if the specificdensity of the mineral/ceramic material is smaller than 0.7 g/cm³ and,preferably, substantially 0.4 g/cm³.

[0013] Preferably, a material based on vermiculite, an Al-Fe-Mg silicatefrom the group of mica minerals, is used, which is rapidly heated toexpel crystal water, whereby the individual laminar layers of thecrystal structure are drifted apart and the originally solid, flatcrystals expand into long, worm-like particles. The thus obtainedgranular material is then mixed with a waterglass-type binder, pressedinto a shaped body and dried, whereupon it can be employed as a shapedpart around which light metal is cast for the production of a cast wheelrim.

[0014] Furthermore, the provision of such a porous silicate shaped partoffers the advantage that, on account of the structure of the silicatematerial, an infiltration will not take place by itself and thus neednot be prevented by the formation of a cast-resistant, closed externalskin on a metallically porous shaped part. Hence, the process control inthe manufacture of cast wheel rims by means of light-metal bodies andcast-in light cores is substantially facilitated.

[0015] In the following, the invention will be explained in even moredetail by way of particularly preferred exemplary embodimentsillustrated in the drawing, to which it is, however, not limited.Therein:

[0016]FIG. 1 shows a sector-shaped section of a cast wheel rim;

[0017]FIG. 2 shows a radial section through this cast wheel rim alongline II-II of FIG. 1, in the region of a spoke of the cast wheel rim;

[0018]FIG. 3 shows a section angularly offset relative to the formersection, along line III-III of FIG. 1 to elucidate the cross section ofthe cast wheel rim in the region of a passage provided between thespokes of the cast wheel rim; and

[0019]FIG. 4 shows a cross section in the region of a spoke of said castwheel rim along line IV-IV of FIG. 1.

[0020] The cast wheel rim 1 illustrated in the drawing and at presentconsidered as particularly preferred (in the following briefly referredto as wheel rim) is comprised of a wheel body 2 configured as acomposite body and including a hub portion 3, a rib portion 4 and a beadportion 5 with a wheel rim base 6. In the hub portion 3, bolt bores 7are conventionally provided to screw-fasten the wheel rim 1 togetherwith the tire mounted thereon, which is not illustrated in detail.

[0021] The wheel rim body 2 is cast of light metal in a conventionalmanner; the present wheel rim is, for instance, a wheel rim cast ofaluminum or magnesium. As is the case with conventional light-metalwheel rims, the light metal for the present wheel rim 1 is substantiallycast in the form of closed “hollow” sections similar to box sections,whereby high strength values can be attained. In order to keep themanufacture as simple as possible, the “hollow” spaces in these boxsections or, generally, in the closed sections of the wheel rim 1 arefilled out by light-weight shaped parts prefabricated of porous silicatematerial in the form of pressed bodies, and subsequently inserted intothe casting tool (not illustrated) during the casting of the wheel rims1.

[0022] By the aid of these shaped parts, the production process issubstantially facilitated as against shaped parts made of metals ormetal foam, since the former offer a temperature resistance exceedingthe casting temperature of usual light metals like aluminum andaluminum-magnesium alloys. The shaped part, prior to casting, can thusbe preheated to a temperature exceeding the casting temperature whilemaintaining its shape. This is of great advantage, because the airenclosed in the shaped part of a low specific mass will not be subjectedto an expansion during casting, which might result in strength-reducinggas inclusions in the light-metal body surrounding the shaped parts.

[0023] In the present exemplary embodiment, a one-piece shaped part 8,i.e. a pressed body, made of porous silicate material is provided, whichis circularly closed in the bead portion at 8′ and constructed in onepiece with radially inwardly projecting spoke shaped parts 81, in therib portion 4, in the region of the rim spokes 9.

[0024] As is apparent from the drawing and, in particular, from FIG. 3as compared with FIG. 2, the shaped part 8, i.e., the circularly closedexternal part 8′, in its portion between the spokes 9 is designed to besmaller in cross section than the portion immediately radially beyondthe spokes 9, wherein the associated bead portion 5 of the wheel rim 1in those circumferential sections also has a smaller cross sectionwhich, via transitional portions 10 and 11, respectively, joins thelarger-thickness sections of in the region of the spokes 9.

[0025] Depending on the shape of the wheel rim - the wheel rim 1illustrated with its spokes 9 is to be regarded as but one of a numberof examples - the shaped parts 8 may, of course, also have differentdesigns and it is, in particular, also possible to provide the shapedparts 8″ in the region of the spokes as parts separated from the annularshaped part 81. It is also conceivable to provide several shaped partsadjacently in a spaced-apart relationship in the rib portion 4 withinthe spokes 9, so that multi-compartment hollow sections will be formedby the light metal during casting. What is important, anyway, is that bycasting light metal around the light-weight pressed-body shaped parts 8and 8′, 8″, respectively, closed box sections are formed as indicated at12 in FIG. 4, whereby high strength values and a substantiallyfacilitated production as compared to metal shaped parts will beobtained.

[0026] In doing so, very thin-walled box sections 12 can be provided ina simple manner by the shaped parts 8 and 8′, 8″, respectively - nospecial measures having to be taken for eventually expanding gas -without affecting their strength. Moreover, the porous pressed-bodyshaped parts 8 or 8′, 8″, respectively, have very low mean specificweights as compared to the light metal used for the wheel rim 1 properand even in comparison with metal-foam shaped parts, so that additionalweight advantages are obtained.

[0027] In experiments silicate-bonded aluminum-iron-magnesium silicatesuch as, e.g., vermiculite, has proved to be particularly advantageousfor the manufacture of shaped parts 8 and 8′, 8″, respectively, yet anaccordingly simplified manufacture as regards the casting into lightmetal is also reached with comparable, similar porous silicate materialsof different types.

[0028] It is, therefore, feasible to economically produce in the regionsconcerned such as, in particular, in the region of the spokes 9 and inthe bead portion 5, cross sections which, by providing porous coreparts, enable at a low specific weight by an extremely simplemanufacture a maximum degree of strength at a minimum of light-metalmass (and hence a minimum weight). Depending on the gas portion, thesilicate materials may have specific weights of, for instance, 0.4 to0.5 kg/dm³ with good results in practical tests having been obtainedwith silicate materials having a specific weight of around 0.45 kg/dm³.For a simple and cost-effective production of the shaped parts 8; 8′,8″, the latter are simply produced by a pressing process; the materialneed neither be sintered nor baked.

[0029] During production, comparatively simple shaping procedures may beenvisaged for the wheel rim 1, wherein, in particular, no bends or thelike are required in the regions concerned, as were provided in the pastin order to increase the strength of the profiled sections; accordingly,also the casting tools for the wheel rims 1 can be designed in arelatively simple manner.

[0030] Prior to the casting of light metal, e.g. cast aluminum, theprefabricated and preheated shaped parts 8 and 8′, 8″, respectively, areinserted into the casting tool and there are fixed in their rightpositions by the aid of centering pins 13, 14. In view of a hightemperature resistance, the centering pins 13, 14 can be made of aceramic material.

[0031] After this, the light metal is cast into the casting tool withthe shaped parts 8 and 8′, 8″ being cast round. The centering pins 13,14, two of which are schematically indicated in FIG. 2, remain in thelight metal of the wheel rim 1, and possible parts protruding from theouter side of the wheel rim 1 are simply ground off after removal fromthe mold.

[0032] It goes without saying that the porous shaped parts 8, 8′, 8″ areto be chosen such that they do not melt as they are cast around by thelight metal. The previously mentioned silicate materials, i.e.preferably Al, Mg and Fe silicates, are well suited for this purpose inthat no adverse penetration of light metal will occur on account oftheir ceramic structures. With porous metallic materials, however, theinfiltration of light metal into the metal body would be prevented onlyby an oxidic skin usually formed during production and having a highermelting temperature than the light metal of the wheel rim body 2. Ifthis were not the case, an overpressure would have to be applied atporous metallic materials in order to prevent their infiltration throughthe light metal.

[0033] The present wheel rim 1 is particularly suitable for passengercar wheels and truck wheels and for motorcycles as well as for wheelsused in aircraft construction.

1. A cast wheel rim (1) including a light-metal body (2) which at leastpartially encompasses at least one shaped part (8, 8′, 8″) forming acast-in core and having a mean specific weight smaller than that of thelight metal used for the casting, characterized in that the shaped part(8, 8′, 8″) is comprised of a pressed body made of a porous silicatematerial.
 2. A cast wheel rim according to claim 1, characterized inthat the silicate material of said pressed body has a temperatureresistance up to a temperature that is higher than the melting point ofthe light metal used for the casting.
 3. A cast wheel rim according toclaim 2, characterized in that the silicate material of the pressed bodyhas a temperature resistance up to at least 1000° C.
 4. A cast wheel rimaccording to any one of claims 1 to 3, characterized in that thesilicate material is comprised of Al-, Mg- and/or Fe-silicates.
 5. Acast wheel rim according to claim 4, characterized in that the silicatematerial is comprised of silicate-bonded aluminum-iron-magnesiumsilicate.
 6. A cast wheel rim according to any one of claims 1 to 5,characterized in that the specific density of the silicate material issmaller than 0.7 g/cm³ and, preferably, substantially 0.4 g/cm³.